Making ocean loop hexagonally
So here is a hexagon grid converted to a staggered rectangular grid with indication of the direction how the rectangles need to "line up":



The rectangles are seamless from top to bottom exactly how you expect. But the left-right 'seamlessness' needs to be rotated +30°(or -30°) because of the staggering.

When you have the rectangle seamless, you create the hexagon from it by cutting and re-arranging the corners like this:



Now you know how to seamlessly tile hexagons. With a bit of skill you don't need to go through the rectangle phase at all, just create tiling with one tiling axis rotated 30°. That's the trick.